Several protocols have been designed for transferring messages to selective call receivers. These protocols include POCSAG (Great Britain's Post Office Code Standardization Advisory Group) and GSC (Golay Sequential Code). A message comprises an address if the message is a tone only message, or an address and information if the message is a data message. The information in a data message conventionally comprised one of several output modes (transmitted in information formats) including numeric (transmitted by BCD), alphanumeric (transmitted by ASCII), or voice (transmitted by digital or analog).
A preamble of a POCSAG signal comprises a number of zero-to-one transitions for bit synchronization. The first word following the preamble is a sync code word which contains a predetermined binary sequence used for frame synchronization. Sixteen words of information, each comprising a selective call address and an associated message, follow before the sync code is repeated. The structure of the addresses and information may be referred to as the signalling format.
In a GSC selective call network, the receivers are divided into a plurality of groups and a twenty three bit code in the preamble selects one of the groups in addition to providing means for bit and frame synchronization. Following the preamble, a start code indicates that the preamble is finished and the information following contains selective call addresses of selective call receivers within the group and messages for those selective call receivers in a pattern of sixteen information words followed by one start code word.
However, in both POCSAG and GSC, as in other known protocols, the information following each of the addresses comprised only one information format. Each address would specify to the selective call receiver receiving that address whether its output mode following would be numeric, alphanumeric, or voice. The selective call receiver would thereby encode the proper information format as transmitted, e.g., BCD or ASCII.
Thus, what is needed is a selective call receiver signalling format having a single address and accommodating two or more information formats.